simulation and contingency analysis of a … · 2.4 optimal capacitor placement and sizing full...

Journal of Engineering and Sustainable Development, Vol. 20, No.04, July 2016 www.jeasd.org( ISSN 2520-0917)

238

SIMULATION AND CONTINGENCY ANALYSIS OF A

DISTRIBUTED NETWORK IN IRAQ

Dr. Thamir M. Abdul-Wahhab

1, Omar Ali Abdullah

2

1) Lecturer, Department of Electrical Engineering, University of Technology, Baghdad, Iraq.

2) M. Sc. Student, Department of Electrical Engineering, University of Technology, Baghdad, Iraq.

Abstract: This paper presents the contingency analysis to study the impact of forced or planned outages

on electrical distribution system. The mathematical modeling of contingency analysis includes; the load

flow analysis and the power restoration analysis. The power restoration is formulated as a constrained

multi-objective optimization problem, based on the ranking search method. The method performs load

flow simulations and utilizes the analytical information obtained to maximize the amount of total power

restored and to minimize the number of required switching operations.In this work the contingency

analysis is based on the advanced CYMDIST software as a tool for the simulation of a distribution

network and performing the required analysis. CYMDIST software is practical and efficient analysis

software used by many electrical companies worldwide as well as by the Iraqi ministry of electricity. The

distribution network simulation and contingency analysis proposed in this paper were implemented on

Al_Amereah 11 kV network which is a part of Baghdad city distribution network. The results show that

full power restoration under contingency conditions after fault isolation without violating constraints was

achieved in three steps: optimal switching, addition of a feeder, and optimal capacitor placement.

Keywords: Contingency analysis in distribution network, CYMDIST software, power restoration,

network reconfiguration, capacitor placement.

العراق في توزيع لشبكة الطوارئ وتحليل محاكاة

على منظومة التوزيع الكهربائية. التمثيل تقدم هذه الورقة تحليل الطوارئ لدراسة أثر انقطاع التيار القسري أو المخطط له: الخالصة

القدرة الكهربائية. استعادة القدرة الكهربائية تم صياغتها سريان الحمل و تحليالت استعادة الرياضي لتحليل الطوارئ يشتمل على تحليالت

هذه ranking search method.لى طريقة البحث حسب الترتيب الطبقي دة,وذلك باالستناد اعلى شكل مسألة أمثلية متعددة االهداف مقي

ا الستعادة اعظم قدرة كهربائية للمستهلكين وبأقل الطريقة تعمل محاكاة لسريان الحمل وتستخدم المعلومات التحليلية التي يتم الحصول عليه

المتقدمة كأداة لمحاكاة CYMDISTعدد من عمليات التبديل )فتح وغلق المفاتيح(.في هذا العمل استند تحليل الطوارئ على برامجيات

برنامج تحليل عملي وفعال يستخدم من قبل العديد من شركات CYMDISTشبكة التوزيع الكهربائية وإجراء التحليالت المطلوبة. برنامج

المقترح في التوزيع الكهربائية وتحليل الطوارئ شبكة الكهرباء في جميع أنحاء العالم, وكذلك من قبل وزارة الكهرباء العراقية. محاكاة

وتشير النتائج أن الكرخ.-من شبكة توزيع كهرباء بغداد والتي تمثل جزءا kV 11على شبكة توزيع كهرباء العامرية هذه الورقة تم تنفيذه

استعادة الخدمة كاملة بعد عزل العطل, بدون أي انتهاك للقيود في ظل حالة الطوارئ, تم تحقيقه في ثالث خطوات: التبديل )فتح وغلق

المفاتيح( االمثل, اضافة ُمغذي, والتوزيع االمثل للمتسعات.

*Corresponding Author [email protected]

Vol. 20, No. 04, July 2016

ISSN 2520-0917

www.jeasd.org

mailto:[email protected]

mailto:[email protected]


239

1. Introduction

Due to the huge expansion of electric power systems the distribution systems have

been more complex and hence fault events are unavoidable. These faults affect the

system's reliability. Contingency analysis studies the impact of outages of network

elements and investigates the resulting effects on bus voltages and power flow for the

remaining system.

In case of feeder outage in a power distribution system, the supply of power is

isolated from the feeder to certain loads. Most feeders are provided with tie circuits to

neighboring feeders from either the same or different substations in order to restore

power to out of surface consumers following a fault. Restoring power using these ties

requires a number of switching operations [1].

The objective of power restoration is to restore the maximum possible loads by

supplying power to the out of service areas from other distribution feeders by finding

the optimum switching plan (changing the status of normally closed sectionalizing

switches and normally open tie switches) this process is known as network

reconfiguration.

Restoring power to the whole out of service area is not always possible, sometimes

substations located at the borders of the utility service area may have no alternative feed

to its feeders. Sometimes alternative feed is possible however it may not be possible to

restore power at peak load intervals without causing over load or voltage drop problems

[2]. The capacity of networks must be expanded over time to cope with increasing

demand arising from population and economic growth. Feeders, transformers and other

network appliances need to be upgraded to support the load growth and peak load level.

However, upgrading the transformer and feeder rating may not be cost benefit. To avoid

extra upgrades, area planning is needed to provide means for restoring the abnormal

system to its normal working condition through [3]:

1) Load balancing in the network, by transferring some loads from heavily loaded

feeders to lightly loaded feeders by switching operations.

2) Placement of shunt capacitors.

3) Replacing the existing conductors with higher capacity conductors.

4) Addition of new feeder to carry some of the loads from the existing feeders.

2. Mathematical Model

2.1 Load Allocation Method

In this work the connected kVA load allocation technique provided by CYMDIST

software is used which distributes the substation load demand (entered by the user in

amperes for each phase) along the feeder according to the connected kVA of the

distribution transformers.

The connected kVA algorithm [4].

kVAT = ∑ KVAC(i)

n

i

× LF (1)


240

kWa(i) = kWd × [KVAC(i)×LF

kVAT] (2)

kVAra(i) = kWa(i) × √(1

P.F)2 − 1 (3)

Where:

i : is the section number. kWd : is the demand (kW).

kVAc: is the connected (kVA). kVAT: is the total connected (kVA).

kWa(i): kW allocated on section (i). kVAra(i): kVAr allocated on section (i).

2.2 Load flow method (Backward/Forward sweep algorithm)

The Backward/Forward sweep algorithm solves the load flow equations of radial

distribution networks iteratively in two stages:

In the first stage the node and branch currents are calculated by the backward sweep

starting from the end nodes back to the source node using Kirchhoff's Current Law

(KCL). The end nodes currents are calculated as a function of the end nodes voltages

and the given loads.

In = (Sn

Vn)

∗

(4)

For the first iteration the initial end nodes voltages are taken as the nominal bus

voltages at these nodes.

The backward sweeps calculates branch currents and voltage drop in branches to

update nodes voltages back to the source node.

Vk = Vn + Zk,n × Ik,n (6)

The calculated branch currents are saved to be utilized in the following forward

sweep calculations.

Finally as a convergence criterion the calculated source voltage is compared to the

specified source voltage for mismatch calculation.

Error = ||Vs| − |V1|| (7)

In the second stage by the forward sweep starting from the source node to the end

nodes the voltage is calculated at each node as a function of the branch currents,

using the currents calculated in the previous backward sweep using Kirchhoff's

Voltage Law (KVL), with the nominal voltage taken as the source voltage at the

starting of each forward sweep.

Vk = Vn − Zk,n × Ik,n (8)


241

The forward and backward sweeps continues until the calculated source voltage

becomes within a specified tolerance with the nominal source voltage [5].

2.3 Power restoration method

In this work the ranking based search method is employed to solve the power

restoration problem as a multi objective function multi constraint optimization

problem, as illustrated in Figure (1). The method acts to find the optimum switching

plan that gives the optimum network configuration which satisfies the objective

functions of maximizing power restoration, minimizing the number of switching

operations, and load balancing to minimize the risk of overload. Without violating

constrains of voltage drop limits, line/transformer capacity limits, and feeder load

limits. Also, the radiality of the feeders should be kept. The constrained optimum

power restoration algorithms are formulated as follows:

2.3.1 The objective functions are

1. Minimization of out of service area:

min 𝑓1(x̅) = ∑ Li

n

i=1

− ∑ Li

nR

i=1

(9)

Where,

x̅ : is the switch status vector of the network,

x̅ = [SW1, SW2 … SWNs]

SWi: is the status of ith switch, closed = 1 and open = 0.

Ns : is the number of switches in the network.

n : is the number of energized buses in the network before fault.

Li : is the load on ith bus.

nR: is the number of energized buses in the restored network.

In equation (9), it is assumed that all the buses in the network from 1 to n are

energized before fault case. While nR is the number of the energized buses after fault

condition.

2. Minimization the number of switching operations:

min𝑓2(�̅�) = ∑|SWj − SWRj|

Ns

𝑗=1

(10)

Where,

x̅ : is the switch status vector of the network,

x̅ = [SW1, SW2 … SWNs]


242

Ns: is the number of switches in the network,

SWj: is the status of jth switch in network just after fault.

SWRj: is the status of jthswitch in the network after restoration.

2.3.2 The constraints

1. Radial network structure: For fault locating and isolation, and the

coordination of protective devices, a radial network structure must be

retained after power restoration.

2. Bus voltages should not violate their limits:

|V min | ≤ |Vj | ≤ |V max | (11)

Where: Vj , is the voltage at bus j; Vmin, is the minimum acceptable bus voltage;

Vmax, is the maximum acceptable bus voltage.

3. Feeders should not be overloaded:

Ij ≤ Ijmax (12)

Where: Ij , is the load current in line j; Ijmaxthe maximum acceptable load

current in line j.

4. Power source limit constraint: The total loads of a certain partial network

cannot exceed the capacity limit of the corresponding power source.

Pt ≤ Psmax. (13)

Qt ≤ Qsmax. (14)

Power factor constraint, harmonics constraint, and voltage angle constraint has not

been taken into consideration to avoid the complexity of the problem.


243

Figure 1. Demonstrates the ranking based search method for power restoration after a contingency case in a distribution network

[6].


244

2.4 Optimal capacitor placement and sizing

Full Power restoration for the out of service area from adjacent feeder may not be

possible because extra power flow on the feeder may lead to over load condition on this

feeder. Placement of controlled capacitor bank can increase the power transfer capacity

of the feeder and increase the possibility of full power restoration. The problem

is formulated to determine the optimal shunt capacitor size and location in a radial

distribution network by minimizing the ohmic losses. At the same time, the choice is

restricted by electric network constraints. The sizes of capacitor banks are given by

standard size, which makes the set of solutions to be discrete. Therefore, the problem is

classified as a discrete optimization problem [7]. Providing reactive power

compensation for a primary distribution network. CYMDIST module is used to

determine an optimal compensation solution which also enables variation of the solution

when the network configuration changes. Applying compensation using the CYMDIST

module helps in saving additional power, improves the voltage profile, and causes lesser

load shedding during restoration

2.4.1 Capacitor placement algorithm

The optimal capacitor size and placement at proper node should minimize the

objective function in equation (15):

Ploss(k+1) ≤ Ploss(k) (15)

Where: PLOSS (K+1), Power losses after capacitor placement; PLOSS (K), Power losses

before capacitor placement.

And satisfy the following constraints:

1. Bus Voltage Limits:

Vmin ≤ |Vi| ≤ Vmax (16)

Where: Vmin Lower bus voltage limit; Vmax Upper bus voltage limit;

|Vi| rms value of the ith

bus voltage.

2. The line flow limits: The line load current (I) should be less than the line rated

current (Irated).

I ≤ Irated (17)

3. Power Conservation Limits: The algebraic sum of all incoming and outgoing

power including line losses over the whole distribution network should be equal

to zero:

PG − ∑ PDni=1 − Plt = 0 (18)

Where: PG is power generation; PD is power demand; Plt is total power losses

4. The number and Sizes of permissible capacitor banks constraint:


245

∑ Qcmi=1 ≤ Qt (19)

Where: Qc, kVAr obtained from the capacitor bank; Qt total reactive power flow

requirement; m total number of capacitor banks.

The proposed method for capacitor placement in a radial distribution feeder is

summarized by the flowchart in Figure (2).

Figure 2. Flowchart of capacitor placement in a radial distribution feeder using CYMDIST program [8].

No

Start

Input data

(R, X, and loads)

Run the load flow analysis for

original feeder

Put Qc at the far end bus from the substation using CYMDIST program

Run the load flow analysis

Vmin ≤ |Vi| ≤ Vmax

I ≤ I(rated)

Add new Qc using

CYMDIST program

Remove Qc and put

prior values of Qc

Run the load flow

analysis

Constraints

satisfied?

Put Qc at the next bus Stop

No

Yes

Yes


246

3. Proposed Network Model

The modeling process begins with acquiring all the input data required for the

modeling, and the combined processed data are entered or imported from GIS software

into CYMDIST to create the distribution system model, with the single line diagram

automatically generated.

4. Contingency Analysis Methodology

The Contingency analysis methodology in this paper is illustrated by the flowchart in

Figure (3). The methodology acts to find the optimal configuration that will maximize

the electrical power restoration to consumers in a distribution network, after fault

isolation, without violating the operational constraints.

Figure 3. Flowchart representing the contingency analysis methodology using CYMDIST software.

Yes

No

No

Start

Create the network model in CYMDIST

Apply load allocation

Analyze the existing network using load flow

Simulate an outage of a feeder or section

Reconfigure the network by switching operations for power

restoration Analyze the new network configuration using load flow

Vmin≤ │Vi│≤Vmax

│Ii│≤ Imax

Optimal network reconfiguration

(maximizing power restored)

End

Yes

Input network data

Optimum network configuration (switches

status)


247

5. Case Study

The analysis is implemented, using the CYMDIST 4.5 (Rev.6) software, on

Al_Amereah distribution network which is a part of the distribution system in Baghdad

city. The network consists of 11 outgoing feeders from Al_Amereah substation

(33/11kV, 2×31.5 MVA) serving a large area of mixed residential, commercial, and

industrial loads. The network is rated at 11 kV, base 100MVA, 50 Hz, with 323 line

sections, 313 buses, and 11 tie switches. The modeling of Al_Amereah network is based

on the actual coordination’s taken from Iraqi Ministry of Electricity (MOE) depending

on the Global Positioning System (GPS) and Geographic Information System (GIS), as

shown in Figure (4).

Loads allocation: Loads are allocated on all sections by using the connected kVA

method depending on the load current at the head of each feeder as given in Table (1).

The secondary (11/0.4 kV) (Delta-Grounded wye) transformer capacities are given in

Table (2).

Figure 4. Al_Amereah network model based on (GPS) and (GIS) data.

Table 1. The load current of the 11 outgoing feeders from Al_Amereah substation.

Table 2. 11\0.4 kV transformer capacities of Al_Amereah network.

Main substation transformer (2)

33/11 kV, 31.5 MVA

Main substation transformer (1)

33/11 kV, 31.5 MVA

P.F. Current/ph (A) Feeder name 11kV P.F. Current/ph (A) Feeder name 11kV

0.85 190 Amereah_87 0.85 10 Amereah_80

0.85 200 Amereah_88 0.85 130 Amereah_81

0.85 260 Amereah_89 0.85 200 Amereah_82

0.85 10 Amereah_90 0.85 220 Amereah_83

0.85 160 Amereah_84

0.85 260 Amereah_85

0.85 100 Amereah_86

Spot load number Transformer

capacity(kVA)

51,158,193,224,227,243,245,255,271 100

8,14,15,17,19,21,22,29,30,34,35,43,45,46,47,48,50,52,53,57,58,61,62,63,65,66,69,

71,73,76,78,80,81,83,85,,86,88,92,94,95,96,97,98,99,106,108,109,110,111,112,116

118,119,120,122,127,129,130,131,132,134,135,136,138,140,141,143,145,146,150,

250


248

5.1 Load flow study of Al_Amereah during normal operation

Voltage levels and load currents are calculated using backward/forward sweep load

flow method in CYMDIST during normal operating conditions for the original

configuration, as shown in Figure (5). The load summary and voltage drop results are

given in Table (3).

Figure 5. Single line diagram of Al_Amereah network during normal operating conditions.

Table 3. Load summary and voltage drop of Al_Amereah network during normal operating conditions.

Feeder

name

Current

A/ phase

Feeder

current

loading

(%)

Total Load P.F.

Minimum

voltage on

feeder

(p.u.)

Location of

minimum

voltage

kW kVAr

Amereah_80 10 2.9 % 161.94 104.35 0.8406 0.999 Section _6

Amereah_81 130 37.68 % 2095.61 1299.84 0.8498 0.994 Section _41

Amereah_82 200 57.97 % 3194.18 1976.22 0.85 0.98 Section _71

Amereah_83 220 63.76 % 3512.49 2178.69 0.8498 0.98 Section _99

Amereah_84 160 46.38% 2573.5 1597.02 0.8497 0.98 Section _112

Amereah_85 260 75.35% 4100.4 2531.86 0.85 0.963 Section _152

Amereah_86 100 29 % 1616.88 1004.6 0.849 0.995 Section _213

Amereah_87 190 55.07 % 3025.56 1874.01 0.85 0.976 Section_251

155,156,160,164,168,183,190,194,204,206,207,208,209,211,213,215,220,221,222,

223,230,237,246,249,250,256,258,260,261,263,265,266,270,275,278,280,283,286,

289,291,297,300,309,313,315,319

13,44,55,60,67,74,75,82,104,105,115,117,125,152,172,180,181,182,202,225,226,

236,238,242,264,267,269,272,273,274,276,279,295,299,305,308,310,317,318

400

9,11,12,68,77,89,176,179,185,187,191,192,195,199,232,233,235,244,247,248,301,

302

630

2,3,6,103,157,175,282,285 1000


249

Amereah_88 200 57.97 % 3198.75 1971.48 0.85 0.98 Section _286

Amereah_89 260 75.4% 4154.27 2557.04 0.85 0.98 Section _319

Amereah_90 10 2.9% 161.95 101.22 0.85 0.999 Section _321

The results obtained in Table (3) show that all the feeders are within their current

carrying capacities, the voltage levels are within their 5% limit, and the network is in a

healthy state.

5.2 Contingency analysis of Al_Amereah distributed network

To perform the contingency analysis, feeder outage is simulated assuming 3-phase

fault on one feeder at a time.

Feeder Amereah_81 outage is simulated by assuming a fault on section_7 which is

the main outgoing line (underground cable) from substation Al_Amereah to supply the

rest of the feeder. The contingency program opens switch (Sw_7) to clear the fault, this

results in loss of power supply to sections (7 to 41), as shown by the darker black line in

Figure (6). The total load for the unserved consumers is 2905.6 kW.

Similarly for feeders Amereah_82, Amereah_84, and Amereah_85 a fault is assumed

on the main section of each feeder, which is the outgoing line (underground cable) from

substation Al_Amereah to supply the rest sections of the feeder. The total load for the

unserved consumers for each case is given in Table (4).The contingency program opens

the corresponding switch to clear fault, this results in loss of power supply to the rest of

the feeder, as shown by the bold black line in Figures (7) to (9).

Figure 6. Single line diagram of Al_Amereah network showing the outage of feeder Amereah_81.



250

Table 4. Summary of contingency analysis following feeder outage.

Feeder outage Fault location Switch opened

to clear fault

Section outage Consumers

unserved (kW) From To

Amereah_81 Section_7 Sw_7 7 41 2095.6




5.3 Service restoration by network reconfiguration after fault isolation

The program carries on network reconfiguration by opening and closing switches

according to the switching optimization technique to restore power to consumers

affected by the feeder outage. The optimum configurations of feeders Amereah_81,

Amereah_82, Amereah_84, and Amereah_85 are obtained as follows:

1. For the contingency case of feeder Amereah_81, the network was reconfigured by

closing N/O tie-switch (Tie_Sw_212), as shown in Figure (10). Closing tie-switch

(Tie_Sw_212) allow transfer of load 2095.6 kW from feeder Amereah_81 to feeder

Amereah_86 after fault isolation.



(Tie_Sw_70) allow transfer of load 1301 kW from feeder Amereah_82 to feeder

Amereah_89 after fault isolation. Opening N/C switches (Sw_58), (Sw_62), (Sw_66)

and (Sw_71) splits load to avoid overloading on feeder Amereah_89.




Figure 8. Single line diagram of Al_Amereah network showing the outage

of feeder Amereah_84.

Figure 9. Single line diagram of Al_Amereah network showing the

outage of feeder Amereah_85.


251

Amereah_83 after fault isolation. Opening N/C switch (Sw_105) split load to avoid

overloading on feeder Amereah_83.




Amereah_87 after fault isolation. Opening N/C switches (Sw_125), (Sw_126), and

(Sw_137) splits load to avoid overloading on feeder Amereah_87.

The summary of power restoration is given in Table (5).

Table 5. Summary of power restoration following contingency analysis for feeders of Al_Amereah network.

Feeder Amereah_81

Section Id Switch Id Action Reason Power restoration(kW) Consumers

unserved(kW)

Amereah_7 Sw_7 0pen Clear fault 0 2095.6

Amereah_212 Tie_Sw_212 Close Transfer load 2095.6 0

Total 2095.6 0

Feeder Amereah_82

Section Id Switch Id Action Reason power restoration(kW) Consumers

unserved(kW)


Amereah_66 Sw_66 0pen Split load 0 3194.2

Amereah_70 Tie_Sw_70 Close Transfer load 1301 1893.2




Total 1301 1893.2

Feeder Amereah_84


unserved (kW)


Amereah_101 Tie_Sw_101 Close Transfer load 1486.1 1087.4


Total 1486.1 1087.4

Feeder Amereah_85


unserved (kW)






Total 2361.2 1739.2


252




253


The results of power restoration following contingency analysis for the 9 feeders of

Al_Amereah network are summarized in Table (6).

Table 6. Power restoration following contingency analysis for the 9 feeders of Al_Amereah network.

Feeder name Total load before fault (kW) Power restored after fault

clearing (kW)

Consumers

unserved (kW)

Amereah_81 2095.6 2095.6 0

Amereah_82 3194.2 1301 1893.2

Amereah_83 3512.5 2082.5 1430

Amereah_84 2573.5 1486.1 1087.4

Amereah_85 4100.4 2361.2 1739.2

Amereah_86 1616.9 1616.9 0

Amereah_87 3025.6 697.1 2328.4

Amereah_88 3198.7 3198.7 0

Amereah_89 4154.3 4154.3 0



254

5.4 Remedial action for further power restoration

Table (6) illustrates that power restoration following contingency analysis for feeders

Amereah_82, Amereah_83, Amereah_84, Amereah_85, and Amereah_87 needs more

remedy. Achieving further power restoration in the distribution system requires;

addition of new switching, or addition of new feeder, or addition of capacitor to the

network.

5.5 Addition of new switches in the network

Feeder Amereah_82: The proposed plan is by adding N/0 switch (Sw_216) between

node Amereah_216 and node Amereah_50 to restore the electrical power from feeder

Amereah_87 to recover the maximum possible consumers load in the affected areas of

feeder Amereah_82, during contingency case. For this contingency case, the network

was reconfigured by closing N/O tie-switches (Tie_Sw_70) and (Tie_Sw_216) and

opening N/C switch (Sw_63) . Closing (Tie_Sw_70) and (Tie_Sw_216) allow transfer

of 985.4 kW and 2208.8 kW from feeder Amereah_87 and Amereah_89 respectively to

feeder Amereah_82 after fault isolation. Opening N/C switch (Sw_63) split load to

avoid overloading on feeder Amereah_89. The reconfiguration is shown in Figure (14).

The summary of power restoration is given in Table (7).

Table 7. The proposed switching plan for feeder Amereah_82 after addition of tie-switch

(Tie_Sw_216).

Section Id Switch Id Action Reason Power restoration

(kW)

Consumers

unserved

(kW)




Amereah_216 Proposed Tie_Sw_216 Close Transfer load 2208.8 0

Total 3194.2 0

Figure 14. Single line diagram of the network after applying the proposed tie-switch (Tie_Sw_216) to

restore electrical power to consumers of feeder Amereah_82 after isolating fault.


255

5.6 Addition of new feeder in the network

Feeder Amereah_85: The remedy of feeder Amereah_85 using optimal switching

and network reconfiguration did not restore the total power during the contingency case.

By investigating the network we proposed addition of a new outgoing feeder from

substation Al_Amereah. This feeder named Amereah_91 is an underground cable, 2850

m length according to GIS data, as shown in Figure (15). This feeder will reduce load

on feeder Amereah_85. The maximum load current on feeder Amereah_85 before

addition of the proposed feeder was 260 A, and after the addition of the proposed feeder

became 123.8 A, and the maximum load of the proposed feeder is 131.8 A. The load for

feeder Amereah_85 before addition was 4100.4 kW and after addition became 1982.06

kW and the load for feeder Amereah_91 is 2108.86 kW.

The contingency analysis was implemented assuming a fault occurrence on feeder

Amereah_85. In this contingency case, the network was reconfigured by closing N/O

tie-switch switch (Tie_Sw_118) allow transfer of load 1982.1 kW from feeder

Amereah_85 to proposed feeder Amereah_91 after fault isolation as given in Table (8).

The reconfiguration is shown in Figure (16).

Table 8. Optimal switching plan for feeder Amereah_85 after addition of the proposed feeder

Amereah_91.

Section Id Switch Id Action Reason Power

restoration

(kW)

Consumers

unserved

(kW)



Total 1982.1 0

Figure 15. Shows the addition of the proposed feeder Amereah_91 to Al_Amereah network.


256

5.7 Addition of capacitor to the network

After the proposed switching plan for feeder Amereah_84 by addition of switch

(Sw_106), still there are unserved consumers 1087.4 kW as given in Table (6). As a

solution to this problem we proposed addition of capacitors on feeders Amereah_83 and

Amereah_84. By using CYMDIST program /capacitor placement analysis the optimum

capacitors required for network remedy are as follows:

1. Addition of 300 kVAr and 200 kVAr capacitors on sections Amereah_79 and

Amereah_87 respectively to feeder Amereah_83.

2. Addition of 450 kVAr capacitor on section Amereah_102 to feeder Aaereah_84.

This capacitor placement restores all power to feeder Amereah_84 after fault, as shown

in Figure (17).

Figure 17. The optimal switching plan following capacitor placement to restore

electrical power to consumers on feeder Amereah_84 after isolating fault.

Figure 16. Single line diagram of the optimal switching plan to restore electrical power to

consumers on feeder Amereah_85 after isolating fault.


257

The network was reconfigured by closing N/O tie-switch (Tie_Sw_101) allowing

transfer of 2573.5 kW from feeder Amereah_83 to Amereah_84, after fault isolation.

The reconfiguration is summarized in Table (9).

Table 9. Optimal switching planAmereah_84 after addtion of capacitor placement.

6. Al_Amereah Network Voltage Profile

The voltage profile obtained before and after optimum configuration (after fault

isolation) of feeders Amereah_81, Amereah_82, Amereah_84, and Amereah_85, as

shown in Figures (18) to (21) for each case.

Figure 18. Voltage profile of feeder Amereah_81, during normal operation and after fault isolation.

.

Figure 19. Voltage profile of feeder Amereah_82, during normal operation and after fault isolation.

Section Id Switch Id Action Reason Power restoration

(kW)

Consumers

unserved

(kW)



Total 2573.5 0


258

Figure 20. Voltage profile of feeder Amereah_84; during normal operation and after fault isolation.

Figure 21. Voltage profile of feeder Amereah_85; during normal operation and after fault isolation.

7. Current Loading of Al_Amereah Network

Figure 22. Current loading for feeder of Al_Amereah_81 network.


259



Figure 25.Current loading for feeder of Al_Amereah_85 network.


260

8. Reactive Power Compensation for Feeder Amereah_83 and Feeder Amereah_84

Table (10) presents current loading, real power, reactive power, and voltage profile

before and after capacitor placement on feeder Amereah_83 and feeder Amereah_84.

Figures (26) to (29) show the downstream reactive power profile with respect to

distance for feeders Amereah_83 and Amereah_84 before and after capacitor

placement.

Table 10. Presents current loading, power, and voltage profile after capacitor placement on feeder

Amereah_83 and feeder Amereah_84.

feeder

Amereah_83

Total load used before compensation Total load used after compensation

Current

A/phase

kW kVAr Minimum

voltage

(p.u.)

Current

A/phase

kW kVAr Minimum

voltage

(p.u.)

System load 220 3512.49 2178.69 0.98 190.3 3512.4

9

2178.69 0.9868

Total adjusted

shunt capacitor

--- 0.0 --- --- --- --- 1465.59 ---

conductor

capacities

--- 0.0 9.29 --- --- --- 9.42 ---

System losses --- 50.02 38.74 --- --- 37.59 29.18 ---

feeder

Amereah_84

Total load used before compensation Total load used after compensation

Current

A/phase

kW kVAr Minimum

Voltage

(p.u.)

Current

A/phase

kW kVAr Minimum

voltage

(p.u.)

System load 160 2573.5 1597.02 0.98 136.5 2573.5 1597.06 0.9915

Total adjusted

shunt capacitor

--- 0.0 --- --- --- --- 1338.57 ---

conductor

capacities

--- 0.0 5.82 --- --- --- 5.83 ---

System losses --- 17.68 14.57 --- --- 13.82 11.64 ---

Figure 26. kVAr profile of feeder Amereah_83 before capacitor placement.


261

Figure 27. kVAr profile of feeder Amereah_83 after capacitor placement.

Figure 28. kVAr profile of feeder Amereah_84 before capacitor placement.

Figure 29. kVAr profile of feeder Amereah_84 after capacitor placement.


262

Section Amereah_72 (2436.71 m length) has 727.79 downstream kVAr / phase before

compensation; this value is reduced to 238.82 kVAr /phase after applying capacitors

placement. Also, Section Amereah_100 (1379.5 m length) has 533.53 downstream

kVAr / phase before compensation; this value is reduced to 87.273 kVAr / phase after

applying capacitors placement. The sections that have capacitors become a source of

reactive power, the overall active and reactive power losses will be reduced and lead to

increasing conductor capacities. The overall P.F. of each feeder is improved as

illustrated in Table (10).

9. Conclusions

Due to the increasing size and complexity of distribution networks, using practical

software for the simulation and analysis of such networks become a necessity.

Contingency analysis is an important analysis since faults cannot be avoided. In this

paper the CYMDIST software is used as a tool for this analysis. The results show that

performing optimal switching operations to isolate a fault and restoring the power for

maximum number of consumers can only be achieved by proper simulation of the actual

distribution network, accurate load flow analysis, and optimal reconfiguration of the

network.

Power restoration to all consumers cannot be achieved due to many constraints such as

lines capacity and operating current and voltage limitations, so different approaches

have been considered in this work for increasing this power restoration, such as addition

of switches in the network, addition of a new feeder, or addition of capacitors. These

remedial actions for the contingency case can also enhance the overall performance of

the network during normal operation.

Abbreviations

In Load current (Amp) at node n

N/C Normally close

N/O Normally Open

Pt Total active power (kW)

Qt Total reactive power (kVAr)

ss Sectionalizing switches

tS Tie switches

tS1 Tie switch with the largest spare capacity

V1 voltage calculated at node 1

Zpath Electrical distance

10. References

1. Thomas E. McDermott. (1998). “A Heuristic Nonlinear Constructive Method for

Electric Power Distribution System Reconfiguration”, Ph.D. Thesis, Department of

Electrical Engineering, University of Blacksburg, Virginia.


263

2. T. D. Sudhakar. (2012). “Power Restoration in Distribution Network Using

MST Algorithms”, Electrical Engineering Department at St. Joseph’s College of

Engineering, pp.286-306.

3. Rajneesh K.Karn, Yogendra Kumar and Gayatri Agnihotri. (2013). “Multi-

Objective Service Restoration Considering Primary Customers using Hybrid

GA-ACO Algorithm”, International Journal of Computer Applications, Vol. 64,

No.3, February.

4. “CYME Reference Manual”, November, 2010.

www.scribd.com/doc/136501684/CYME-502-Ref-EN-V1-2

5. William H. Kersting. (2002). “Distribution System Modeling and Analysis”,

Chemical Rubber Company (CRC Press) LLC Book, New York Washington.

6. Karen Nan Miu, Hsiao-Dong Chiang, Bentao Yuan and Gary Darling. (1998).

“Fast Service Restoration for Large-Scale Distribution Systems with Priority

Customers and Constraints”, IEEE Transactions on Power Systems, Vol. 13, No.

3.

7. Héctor Marañón Ledesma. (2013). “Optimization of Capacitor Banks in the

Skagerak Networks Transmission Grid”, M. Sc. Thesis, University of Agder.

8. P. Divya and G. V. Siva Krishna Rao. (2013). “Proposed Strategy for Capacitor

Allocation in Radial Distribution Feeders”, International Journal of Research in

Engineering & Technology, Vol. 1, August.

http://www.scribd.com/doc/136501684/CYME-502-Ref-EN-V1-2

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